# CVE-2026-64431: linux: In the Linux kernel, the following vulnerability has been resolved:  ntfs: avoid calling post_write_mst_fixup() for i...

CVE-2026-64431 is fixed in linux on 1 platform by DEBIAN-CVE-2026-64431 (version 7.1.4-1), released August 7, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-64431
- Priority: High
- CVSS: 7.8 (high)
- EPSS: 0.0017
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jul 25, 2026

## Description

In the Linux kernel, the following vulnerability has been resolved:  ntfs: avoid calling post_write_mst_fixup() for invalid index_block  ntfs_icx_ib_sync_write() calls post_write_mst_fixup() when ntfs_ib_write() returns an error, intending to restore the buffer after a failed write.  However, ntfs_ib_write() returns an error immediately if pre_write_mst_fixup() validation fails. The caller, ntfs_icx_ib_sync_write(), interprets any error as a write failure requiring rollback. It does not differentiate between I/O errors and validation failures, and calls post_write_mst_fixup() anyway.  Since post_write_mst_fixup() assumes that the index_block contents is correct, it doesn't perform the boundary checks, which results in out-of-bounds memory access.  An attacker can craft a malicious NTFS image with:   - large index_block.usa_ofs offset, pointing outside the ntfs_record   - index_block.usa_count = 0, causing integer underflow   - or index_block.usa_count larger than actual number of sectors in the     ntfs_record, causing out-of-bounds access  KASAN reports describing the memory corruption:   ==================================================================   BUG: KASAN: slab-out-of-bounds in post_write_mst_fixup+0x19c/0x1d0   Read of size 2 at addr ffff8881586c9018 by task p/9428   Call Trace:    <TASK>    dump_stack_lvl+0x100/0x190    print_report+0x139/0x4ad    ? post_write_mst_fixup+0x19c/0x1d0    ? __virt_addr_valid+0x262/0x500    ? post_write_mst_fixup+0x19c/0x1d0    kasan_report+0xe4/0x1d0    ? post_write_mst_fixup+0x19c/0x1d0    post_write_mst_fixup+0x19c/0x1d0    ntfs_icx_ib_sync_write+0x179/0x220    ntfs_inode_sync_filename+0x83d/0x1080    __ntfs_write_inode+0x1049/0x1480    ntfs_file_fsync+0x131/0x9b0   ==================================================================   BUG: KASAN: slab-out-of-bounds in post_write_mst_fixup+0x1aa/0x1d0   Write of size 2 at addr ffff8881586c91fe by task p/9428   Call Trace:    <TASK>    dump_stack_lvl+0x100/0x190    print_report+0x139/0x4ad    ? post_write_mst_fixup+0x1aa/0x1d0    ? __virt_addr_valid+0x262/0x500    ? post_write_mst_fixup+0x1aa/0x1d0    kasan_report+0xe4/0x1d0    ? post_write_mst_fixup+0x1aa/0x1d0    post_write_mst_fixup+0x1aa/0x1d0    ntfs_icx_ib_sync_write+0x179/0x220    ntfs_inode_sync_filename+0x83d/0x1080    __ntfs_write_inode+0x1049/0x1480    ntfs_file_fsync+0x131/0x9b0   ==================================================================  Let's move the post_write_mst_fixup() call to ntfs_ib_write(). The ntfs_ib_write() function calls pre_write_mst_fixup() at the beginning. If the index_block contents is invalid, pre_write_mst_fixup() fails and ntfs_ib_write() returns early without calling post_write_mst_fixup() on bad index_block.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 14 | 7.1.4-1 | [DEBIAN-CVE-2026-64431](https://patchblox.com/security/data/fix/linux/debian-cve-2026-64431.md) | Aug 7, 2026 |

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Data as of 2026-11-08T13:06:02Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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